The overall objective of our research is to understand the course of differentiation of human erythroid cells in terms of membrane glycoproteins and to evaluate cell membrane glycoproteins as onco-differentiation cell surface markers shared by tumor cells and normal cells at an early stage of differentiation. Two major aspects deal with: (1) Testing whether certain membrane glycoproteins can function as tumor-specific markers as well as normal immature cells. We have found that tumor promoters diminish the expression of Gp105 on K562 cells, whereas they produce less glycosylated Gp105 in HEL cells. The results indicate that the expression of Gp105 is closely related to the status (immature or macrophage-like cells) of cells treated by tumor promoters. Studies are in progress to understand these results in terms of de novo biosynthesis. (2) Clarifying structure change of lactosaminoglycan throughout the various ontogenic and oncogenic stages. We have found that lactosaminoglycan displays a drastic structural change during ontogenesis and differentiation. We have recently elucidated the structure of lactosaminoglycan present in human neonatal erythrocytes and mature granulocytes with the help of a newly developed technology, fast atom bombardment mass spectrometry. Further studies will elucidate the structures of lactosaminoglycan isolated from adult erythrocytes and glycopeptides from human erythroleukemic cells. (M)